Atlas of pathophysiology, 2 Edition

Part II - Disorders

Respiratory Disorders 

Emphysema

Emphysema, a form of chronic obstructive pulmonary disease, is the abnormal, permanent enlargement of the acini accompanied by destruction of alveolar walls without fibrosis. Obstruction results from tissue changes rather than mucus production, which occurs in asthma and chronic bronchitis. The distinguishing characteristic of emphysema is airflow limitation caused by lack of elastic recoil in the lungs.

Age Alert

Aging is a risk factor for emphysema. Senile emphysema results from degenerative changes that cause stretching without destruction of the smooth muscle. Connective tissue isn't usually affected.

Causes

·   Cigarette smoking

·   Deficiency of alpha1-antitrypsin

Pathophysiology

Primary emphysema has been linked to an inherited deficiency of the enzyme alpha1-antitrypsin, a major component of alpha1-globulin. Alpha1-antitrypsin inhibits the activation of several proteolytic enzymes; its deficiency is an autosomal recessive trait that predisposes a person to emphysema.

In emphysema, recurrent inflammation is associated with the release of proteolytic enzymes from lung cells. This causes irreversible enlargement of the air spaces distal to the terminal bronchioles. Enlargement of air spaces destroys the alveolar walls, which results in a breakdown of elasticity and loss of fibrous and muscle tissue, making the lungs less compliant.

The alveolar septa are initially destroyed, eliminating a portion of the capillary bed and increasing air volume in the acinus. This breakdown leaves the alveoli unable to recoil normally after expanding and results in bronchiolar collapse on expiration. The damaged or destroyed alveolar walls can't support the airways to keep them open. The amount of air that can be exhaled passively is diminished, trapping air in the lungs and leading to overdistention. Hyperinflation of the alveoli produces bullae and air spaces adjacent to the pleura.

Signs and symptoms

·   Tachypnea

·   Dyspnea on exertion

·   Barrel chest

·   Prolonged expiration and grunting

·   Crackles and wheezing on inspiration

·   Decreased breath sounds

·   Hyperresonance

·   Clubbed fingers and toes

·   Decreased tactile fremitus

·   Decreased chest expansion

·   Chronic cough with or without sputum production

·   Accessory muscle use

·   Mental status changes, if carbon dioxide retention worsens

Diagnostic test results

·   Chest X-rays in advanced disease show a flattened diaphragm, reduced vascular markings at the lung periphery, overaeration of the lungs, a vertical heart, enlarged anteroposterior chest diameter, and a large retrosternal air space.

·   Pulmonary function studies indicate increased residual volume and total lung capacity, reduced diffusing capacity, and increased inspiratory flow.

·   Arterial blood gas analysis usually reveals reduced partial pressure of arterial oxygen and a normal partial pressure of arterial carbon dioxide until late in the disease process.

·   Electrocardiography shows tall, symmetrical P waves in leads II, III, and aVF; a vertical QRS axis and signs of right ventricular hypertrophy are seen late in the disease.

·   Complete blood count usually reveals an increased hemoglobin level late in the disease when the patient has persistent, severe hypoxia.

Treatment

·   Avoidance of tobacco smoke and air pollution

·   Bronchodilators, such as beta-adrenergic blockers, albuterol, and ipratropium bromide

·   Antibiotics

·   Flu vaccine to prevent influenza

·   Pneumovax to prevent pneumococcal pneumonia

·   Adequate hydration

·   Chest physiotherapy

·   Oxygen therapy

·   Mucolytics

·   Aerosolized or systemic corticosteroids

·   Lung volume reduction surgery

·   Lung transplantation

P.91

LUNG CHANGES IN EMPHYSEMA

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